This invention relates to hydraulic cylinders and in particular to hydraulic master cylinders used, for example, to operate vehicle clutches.
Such a cylinder, hereinafter referred to as of the type specified, comprises a piston with a seal in sealed sliding contact within a bore to define a working chamber ahead of the piston for the discharge of pressurised fluid from the bore via an outlet when the piston is undertaking a working stroke, an inlet is provided into the bore from an associated reservoir to allow connection between the reservoir and the working chamber when the piston is in a fully retracted state for recouperation of fluid from the reservoir to the working chamber.
Many arrangements have been provided for allowing such recouperation and it is an object of the present invention to provide a simple and low cost construction for recouperation.
Thus according to the present invention there is provided a hydraulic cylinder of the type specified in which the connection between the reservoir and working chamber is provided via a sleeve in the bore which includes anally extending grooves, said grooves being closed by the piston seal during a working stroke of the cylinder but the ends of the grooves being open when the piston is in a fully retracted condition within the sleeve thus by-passing the piston sleeve to connect the working chamber and reservoir.
The arrangement of the present invention is particularly suitable for clutch master cylinders in which the master cylinder body is manufactured from plastics material and the sleeve is also of plastics material.
The sleeve may also have a secondary function of providing an abutment for a return spring which returns the piston to its fully retracted position when an operating pedal associated with the piston is released.